The present invention relates to a delivery safety apparatus for a sheet-fed printing press wherein a sheet pile height exceeding a predetermined position for sheets sequentially delivered and stacked on a delivery table is detected in the sheet-fed printing press, and the delivery table is safely automatically moved downward.
A vertically movable delivery table suspended by lifting chains at four corners thereof is arranged in a delivery apparatus in a sheet-fed printing press. At the start of printing, a pallet which can be lifted by a lift arm or the like is placed on the delivery table. Printed sheets are conveyed while their leading edges are gripped by grippers of delivery chains. The trailing edge of each printed sheet is sucked by a suction wheel at the end of conveyance, so that the printed sheet is decelerated. The printed sheets are released from the grippers above the pallet and are aligned by a jogger and dropped (delivered) on a pile board disposed on the pallet. In this case, the delivery table is controlled to be automatically moved downward while the sheets are stacked on the pile board. In the conventional delivery apparatus for a sheet-fed printing press, a delivery table lifting unit for controlling vertical movement of the delivery table generally includes a mode selection switch for selecting an automatic operation mode or a single operation mode. When the operation mode selection switch is set in the automatic operation mode, a detection signal from a delivery height detector for detecting a height of a pile of sheets stacked on the pile board on the delivery table is generated. The delivery table is automatically moved downward to prevent the height of the stacked sheets from exceeding the predetermined position on the basis of the detection signal.
When a predetermined number of sheets are stacked on the pile board on the delivery table, the next pile board is set to prevent offset of the printed sheets when the predetermined number of printed sheets are stacked on the pile board. The next pile board is set in the single operation mode wherein vertical movement of the delivery table can be arbitrarily performed. Therefore, the delivery table is moved downward by a predetermined amount, and a new pile board is set.
In the conventional delivery apparatus as described above, when a new pile board is set, the operation mode selection switch must be reset from the single operation mode to the automatic operation mode. However, if an operator forgets to change the mode from the single operation mode to the automatic operation mode and if printed sheets exceeding a predetermined number of printed sheets are stacked on the pile board, no detection signal is generated by the delivery height detector. Therefore, the delivery table cannot be automatically moved downward. The stacked sheets are disturbed by the gripper shaft to interrupt printing. In the worst case, the printing press is damaged.
Even in the automatic operation mode, if the delivery table is not automatically moved downward, When an accidental failure occurs, the same inconvenience as described above occurs.